How can I set Regular Expression on TextBox?

Question

How can I set a regular expression on WPF TextBox? I want the textbox to accept input in some predefined format. Is it possible?

Answer 1

You have several options:

• You can create a ValidationRule subclass (see below) and add it to your Binding's Validators property
• You can set a ValidationCallback on your bound property, throw an exception if the value is wrong, and use this technique for easily showing validation errors
• You can create an attached property that registers an event handler for the TextBox.TextChanged property and implement your own validation error notification mechanism
• You can use a normal TextBox with an TextBox_Changed handler in code behind
• You can handle PreviewKeyDown and PreviewTextInput from an attached property as shown here
• You can use a masked text box as mentioned by Jan

For arbitrary regexes I would generally use WPF's built-in validation features or do the validation on the bound property. For specific needs the PreviewKeyDown/PreviewTextInput or masked text box might be better.

Here is how you would create a ValidationRule subclass:

public class RegexValidationRule : ValidationRule
{
  ... // Declare Regex property and Message property

  public override ValidationResult Validate(object value, CultureInfo cultureInfo)
  {
    if(Regex.IsMatch((string)value))
      return ValidationResult.ValidResult;
    else
      return new ValidationResult(false, Message);
  }
}

Answer 2

Either you can check at the changed event or you could use what's called a masked textbox.